With so much discarded tech, we're seeing an increasing number of artists turning to scrap as a medium. San Fransisco-based Constantine Zlatev, uses industrial scrap, surplus tech, and open-source electronics -- and he's using it to tell a message about the evil of war.

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"In the past, the classical artists worked primarily with natural materials. Now, we have mountains of discarded technology," Zlatev explained. "The junkyards are the modern-day quarries, and artists like me can make anything out of these resources."

The Last Gun and Chifte Kavali ('double barrel flute') have been crafted of disabled shotguns, repurposed into mechano-robotic flutes. The barrels of each gun have been drilled with holes to sound notes when compressed air is blown into them, with stoppers controlled by Arduino microprocessors and, in the case of The Last Gun, a Raspberry Pi board.

Each is programmed to play music based on the annual rise and fall of US arms exports from 1960 to 2009. For The Last Gun, the programming is simple: for every fall in exports, it plays a cheerful, upbeat melody; for every rise, the music grows more sombre.

For Chifte Kavali, the gun-flute plays more recognisable music. For every rise in exports, the instrument plays Eric Bogle's "The Band Played Waltzing Matilda", a song Zlatev characterises as carrying a "powerful anti-war message". For every fall, it plays Beethoven's Ode to Joy.

Of Chifte Kavali, Zlatev said, "[It was] created in the shape of a futuristic robotic arm which holds a shotgun, an instrument of discord, and transforms it into a harmonious flute, an object that plays music as a symbol of our wisdom, intellect and humanity."